The following U.S. Patent Applications by the same inventor, Elbert L. McKague, Jr. are being simultaneously filed and incorporated herein by reference: U.S. Patent Application entitled xe2x80x9cApparatus And Method For Controlled Damage Of Conformable Materialsxe2x80x9d; U.S. Patent Application entitled xe2x80x9cComposite Structural Panel with Undulated Bodyxe2x80x9d; and by the same inventor together with inventors Ronald P. Schmidt and David T. Uhl, U.S. Patent Application entitled xe2x80x9cComposite Material Support Structures With Sinusoidal Webs And Method Of Fabricating Samexe2x80x9d.
1. Technical Field
The present invention relates in general to an improved structural member, and in particular to an improved structural beam, made by joining dissimilar materials. Still more particularly, the present invention relates to a structural composite preform for joining the web of a structure with flanges formed from dissimilar materials.
2. Description of the Prior Art
Structural support spars or I-beams typically have an xe2x80x9cIxe2x80x9d or xe2x80x9cHxe2x80x9d shaped cross-section, having a web with a crossbar or flange on each end of the web. The web and flanges extend integrally down the length of the beam, but may vary in shape, thickness, materials, etc. For example, one type of beam has a web formed from a first material (such as a metal) and flanges formed from a second, dissimilar material (such as a composite material). This type of beam has been pursued through a variety of design and manufacturing approaches since these structures offer the potential of providing excellent stiffness and strength-to-weight performance.
Prior approaches to joining dissimilar materials such as metals and composites have generally relied on mechanical fastening if the two elements are at an angle. As shown in FIG. 1, a spar 11 having an inverted T-shaped metal panel 13 with a flange 15 is joined to a flat composite plate 17 with mechanical fasteners 19 such that metal panel 13 and composite plate 17 are perpendicular to each other. In such an arrangement, metal panel 13 must have flange 15 to enable fastening to composite plate 17. Moreover, the necessity of having flange 15 on metal panel 13 adds considerable cost to its fabrication since flange 15 significantly increases the volume of metal that must be purchased and then machined away. In addition, mechanical fastening involves drilling and countersinking holes, installing fasteners and, in some cases, treating the fastener heads to achieve a desired surface smoothness. These steps are expensive and can contribute an additional 25% to 60% to the overall cost of the spar assembly. Thus, an improved apparatus and method for forming a structural support member by joining dissimilar materials at an angle is needed.
A preformed component or xe2x80x9cpreformxe2x80x9d for a structural support beam has a planar base with two longitudinal legs extending in parallel therefrom. A channel is defined between the legs of the preform, and a flat panel that forms the web of the structural support beam is inserted into the channel. The preform is a composite material having continuous filaments of woven or braided fiber. The preform is impregnated with a thermoset resin that joins and bonds the web to the flange of the structural support beam. The preform provides excellent structural support even if the web and the flange are formed from dissimilar materials such as metal and composite. The resin is structurally reinforced with oriented fibers in such a manner as to provide coupling strength between the joined members.
When a single filament is chosen for the preform, its properties are selected to minimize the difference in thermal expansion coefficients of the metal web and the composite flange. However, the preform may have two or more types of filaments with different properties. The filament in the base of the preform is chosen such that its axial thermal expansion coefficient matches that of the composite flange. The filament in the legs of the preform is chosen such that its axial thermal expansion coefficient matches that of the metal web. These filaments are used in combination to provide coupling strength between the joined metal web and composite flange by having the best structural fiber oriented parallel to the legs of the preform, and by its being interwoven into the base of the preform.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.